Having only one source of nutrition, newborn mammals rely absolutely on milk from their mothers for their life (growth) before they are able to digest more diverse foods including solid feedstuffs. In addition, as the amount of milk from their mothers decreases, the young start to ingest solid feedstuffs to supplement insufficient nutrients therein. Weaning is the process of gradually introducing the young to what will be their adult diet and withdrawing the supply of milk. The young are considered to be fully weaned once they no longer receive any breast milk and begin to rely on solid foods for all their nutrition. In dairy farming, which primarily targets the production of milk, much effort has long been made to increase the daily production of milk from the mother cows higher than the amount that calves require and to maintain the production of milk at a high rate before subsequent parturition. For example, mother cows are prevented from suckling newborn calves on parturition day, in order to produce dairy products. Instead, the newborn calves are fed manually with expressed mother's milk, called artificial milk feeding.
Conventionally, dairy farmers feed calves with milk at a dose of 2 kg twice a day, amounting to 4 kg in total, using a milk bottle, or at a dose of 1.5 kg three or four times a day, amounting to 10% of the body weight in total.
With recent increasing interest in the welfare of young calves, attempts have been made to allow them to be fed with milk without restriction. When young calves have free access to artificial feeders or the udders of mother cows, they are observed to suckle 10 times a day at an amount of 10 kg in total. It is reported that 180 to 200 days after birth, however, the body weight of the calves which have been freely fed is not actually different from that of calves which have been restrictively fed a maximum amount of 10% of the body weight.
All such conventional suckling methods are disadvantageous in that because they are suddenly weaned from the milk, the young calves are not sufficiently adapted to the ingestion of solid feedstuff (fodder, hay, etc.) and thus are subject to malnutrition for a considerable period of time, which may lead to insufficient growth or immunodeficiency.
Particularly, calves which used to be satiated with milk undergo greater stress and thus require a longer time period to recover from stress. Dairy farmers are reluctant to allow young calves to freely approach udders or milk bottles for the following reasons. It takes a lot of labor to separate newborns from the mother cow every time suckling occurs. Also, the production of milk from the cows is reduced. Further, upon weaning, the young calves undergo psychological stress in addition to physical stress, so that they may become physically weak.
The problem of the conventional suckling methods resides in the fact that young calves are weaned without being sufficiently adapted to solid feedstuff, or such that they are undernourished. Therefore, there is a need for a precise suckling method that can minimize the weaning stress of calves, and for a system therefor.